C++ execution order when passing function arguments

Question

A container class with the following interface:

template <typename T> class DynArray {
  /// Returns the number of elements in the array.
  inline size_t GetCount();
  /// Releases the internal memory from the \class DynArray
  /// and returns it. The memory must be deallocated manually.
  inline T* Release();
}

In a function call like

SomeFunction(arr.GetCount(), arr.Release())

I would have expected arr.GetCount() to be called before arr.Release(), but the reverse seems to actually happen causing the first parameter to be passed a value of 0 instead of the actual array size. I'm using Visual Studio 2012.

Does the C++ standard say anything specific about order of execution when evaluating function parameters?

The standard does not mandate the order of execution when passed as params, this is left to the implementor: http://stackoverflow.com/questions/2934904/order-of-evaluation-in-c-function-parameters — EdChum, May 20 '15 at 10:59

score 3 · Accepted Answer · answered May 20 '15 at 11:01

It says that the order is entirely unspecified.

The sequencing rules are far too complex to reproduce here, and it's hard to prove a negative, but a non-normative note conveniently summarises it for us:

[C++11: 5.2.2/4]: When a function is called, each parameter (8.3.5) shall be initialized (8.5, 12.8, 12.1) with its corresponding argument. [ Note: Such initializations are indeterminately sequenced with respect to each other (1.9) — end note ] [..]

(Identical text in C++14.)

C++ execution order when passing function arguments

1 Answers1